1. Field of the Invention
The present invention relates to a laser pointing apparatus and in particular, to a laser pointing apparatus having a small size and small weight and capable of controlling a high-accuracy positioning. Moreover, the present invention relates to an on-fulcrum movement drive apparatus for use in the laser pointing apparatus and an antenna and a mirror which are located in an outer space.
2. Description of the Related Art
[A] Firstly, explanation will be given on a conventional laser pointing apparatus.
A laser beam machining apparatus and a laser display apparatus, a laser scan apparatus, and the like, in general, employ a laser pointing apparatus for controlling a laser beam emission angle or a laser beam incident angle.
In most of the conventional laser pointing apparatuses, two mirrors are used in combination for scanning a two-dimensional plane with a laser beam. However, there is a strong desire for reduction in the apparatus size and production cost as well as for simplification of a procedure for optical axis matching and positioning.
In order to satisfy these requirements, for example, Japanese Patent Publication (Unexamined) A-7-185866 discloses an apparatus including a single mirror, a rotary support member which can rotate around a normal axis of the mirror, and a mirror positioning mechanism supported by the support member. In this apparatus, a two-dimensional plane can be scanned by a laser beam using the single mirror.
Hereinafter, explanation will be given on some examples of conventional laser pointing apparatus with reference to the attached drawings.
FIG. 21 is a side cross sectional view of a conventional laser pointing apparatus including: a mirror 101; an electromagnetic exciter 105 for moving the mirror 101; a rotary support member 106 for supporting the mirror 101 and the electromagnetic exciter 105; and a motor rotating the rotary support body 106.
The mirror 101 can be deflected around the Z axis by rotation of the rotary support member 106 driven by the motor 109 and also deflected around the oscillation center 103. This enables a laser beam to scan any position on a two-dimensional plane with the single mirror.
[B] Next, explanation will be given on a conventional on-fulcrum movement drive apparatus.
An antenna mounted on an artificial satellite or other space object is positioned by an on-fulcrum movement drive apparatus so as to assure a preferable communication with an earth station. The on-fulcrum movement drive apparatus moves the antenna around the X axis and Y axis which vertically intersects the X axis. Conventionally, this positioning around two axes has been effectuated by using a support mechanism having two bearings arranged vertical to each other. Moreover, this type of on-fulcrum movement drive apparatus is employed not only for an antenna but also for positioning a mirror and driving a positioning table.
In general, for the apparatuses to be mounted on an artificial satellite, there is a strong requirement for reduction in size and weight. The on-fulcrum movement drive apparatus has also been improved in various ways to satisfy the aforementioned requirement. For example, Japanese Patent Publication (Unexamined) A-53-34499 discloses an on-fulcrum movement drive apparatus in which an object to be driven is supported at a single point of a spherical bearing.
FIG. 22 is a cross sectional view of such a conventional on-fulcrum movement drive apparatus. The on-fulcrum movement drive apparatus shown in FIG. 22 includes: an antenna 301 as an object to be positioned; a spherical bearing 302 for movably supporting the antenna 301; a piston 303 for driving the antenna 301; a linear motor 304 for driving the piston 303; a sensor 305 for detecting displacement of the linear motor 304; and a spring 306 for pushing the antenna 301 toward the piston 303.
According to a detection result of displacement detected by the sensor 305, the linear motor 304 drives the piston 303 and the antenna 301 is moved around the spherical bearing 302 as a fulcrum.
Although not depicted, another set of a piston, a linear motor, and a sensor is arranged in a direction vertically intersecting the drive direction of the piston 303. Thus it is possible to obtain a movement around two axes.
However, the conventional laser pointing apparatus and the conventional on-fulcrum movement drive apparatus have following problems.
[A] Firstly, explanation will be given on the problems involved in the conventional laser pointing apparatus.
The first problem is that the conventional laser pointing apparatus is too large in size because it employs an electromagnetic exciter and a motor having a large volume.
The second problem is that the apparatus is too heavy because the rotary support member requires a comparatively high support strength and becomes heavy. Accordingly, the motor for driving the rotary support member also becomes heavy.
The third problem is that a large power consumption is required. This is because rotation of the mirror around the normal requires rotation of not only the mirror but also the large-mass positioning mechanism constituted by the electromagnetic exciter and the rotary support member.
The fourth problem is that it is difficult to control a pointing position with a high accuracy. This is because the rotation is driven by a motor and a belt. That is, non-linear elements such as the motor torque ripple and the belt expansion/shrinking are involved in the control system.
[B] Next, explanation will be given on the problems involved in the conventional on-fulcrum movement drive apparatus.
The first problem is that it is difficult to control positioning with a high accuracy. That is, the spherical bearing 302 cannot eliminate fluctuation and friction. During a drive, non-linear external components are involved in the control system, lowering the positioning accuracy.
The second problem is that the conventional on-fulcrum movement drive apparatus cannot be used in an outer space. In order to maintain a predetermined sliding characteristic on the spherical bearing 302, a certain amount of lubricant should be present. However, this is difficult in an outer space where a lubricant easily volatilizes.